Fon belongs to the Gbe cluster, a chain of closely related varieties running along the coast and inland from southeastern Ghana through Togo and southern Benin into southwestern Nigeria. Ewe, Gen, Aja, Gun and Fon are its principal members, and the boundaries between them are political and cultural at least as much as linguistic. Gbe sits in the Kwa branch of Niger-Congo.
It is tonal, and tone does grammatical as well as lexical work, so a transcription that omits tone marks loses information that a reader of ritual texts needs. Its morphology is largely isolating: relations that a European language would carry in endings are carried by separate words and by serial verb constructions, where a string of verbs shares one subject and describes one complex event.
Fon rose to prominence with the kingdom that spoke it. Dahomey, centred on Abomey, expanded southward to the coast in the eighteenth century and took the ports through which the Atlantic trade in captives ran, and the language of the court became a language of consequence along the whole Slave Coast. It is written today in a Latin alphabet extended with the additional letters and tone marks of the Africa alphabet, an orthography introduced in the twentieth century. There was no indigenous script.
Fon is now the most widely spoken language of Benin, used as a lingua franca in the south well beyond the communities that hold it as a first language, while French remains the language of the state and of schooling.